Climatic variabilities of potential rainwater savings: A case study for Adelaide

For determining potential water savings from a rainwater tank, a daily water balance method is often seen as the most feasible option with reasonable accurate estimations. However, most of the relevant studies were conducted using continuous simulations of historical daily data for a long period and report an average of cumulative historical water savings. Reporting averaged variables may result in rainwater tank users not getting an adequate insight of the expected variability of water savings. With the impacts of climate change, such variability ranges of outcomes are expected to increase. This paper presents analyses from a newly developed daily water balance model (eTank), which calculates rainwater tank outcomes under three different climatic conditions (i.e. dry, average and wet years). Fifteen representative years (five for each dry, average and wet condition) were selected from historical rainfall data to investigate the impact of climate variability on potential water savings.. An Australian major coastal city, Adelaide, was selected as a case study. eTank results for potential rainwater savings were compared with the another available daily water balance model (Raintank Analyzer), which is widely used by local government authority in South Australia for policy making. 'RainTank Analyser' uses historical daily rainfall data for a long period and reports an average of cumulative historical water savings. Calculations were performed using daily rainfall data from 'Adelaide Airport' raingauge station, considering same conditions in regard to daily rainwater demand, roof area, losses and tank volume. It was found that 'Raintank Analyzer' calculated potential savings are comparable with eTank calculated potential savings in average year only. eTank identified significant variations were between dry, average and wet years except for very few cases (i.e. smaller roof with low demand)